It is known that the direction of magnetization of a magnetic material can be reversed or switched by impressing an external magnetic field of opposite polarity on the material, however, the magnitude of such an external bias field must be relatively high to ensure not only the nucleation by coherent rotation of a domain wall, which separates adjacent regions of the material where each region has an opposite direction of magnetization, but also the propagation of the domain wall through the material until the desired reversal of magnetization direction is obtained. It is well known that in regions of material further from the source of the external field, an increased magnetic field is required to complete the desired propagation of the domain wall through the material. For example, see the following prior art teachings of reversal or switching the direction of magnetization by the use of an externally applied field: see Fast Switchable Magneto-Optic Memory-Display Components; U.S. Pat. Nos. 3,715,736 and 4,114,191. Another prior art teaching (British Pat. No. 1,180,334) uses both an external field and coincident current select of pixels or posts in a magneto-optic display.
A requirement continues for a relatively high external field to accomplish a desired reversal or switching of the direction of magnetization in magnetic materials that support magnetic domains. The nucleation, and the displacement or propagation of a magnetic domain wall in a magnetic material, such as garnets, requires an applied magnetic field. The applied field is generally to the magnetization of the magnetic material. In certain magnetic materials having a high anisotropy, the applied field required to change the direction of magnetization, i.e. magnetic switching, is relatively large; for example, certain films of magnetic material exhibit switching field values in excess of 16,000 Oersteds (Oe). However, it is also known that the switching field required to nucleate a magnetic reversal is relatively large in comparison to that required to displace or propagate the magnetic domain wall which results from the act of nucleating. It would be beneficial to change the magnetic properties of such a magnetic material to alter its switching threshold and, therefore, require an applied switching field of lower value; for example, less than 1000 Oe. This would be useful for a number of systems that use magnetic materials such as computer bubble memories and magneto-optic displays.
In a best mode of the invention, a high anisotropy magnetic material has the magnetic properties altered in a first region of the material so that the first region exhibits a relatively low anisotropy characteristic. The first region is exchange coupled to the remainder of the material at an interface that permits the displacement of a magnetic domain wall through the interface from the first region to the remainder of the material so that the direction of magnetization of the material can be changed or switched through an applied field having a relatively small value.